The invention relates to protectors for protecting the ends of pipe, and particularly for protecting the threads on the ends of pipe.
Pipes, such as pipes used for oil and gas drilling and production, are often produced in sections and are connectable at their ends. One type of connection involves the use of a male threaded portion at one end (the pin end) of a section of pipe that is threadingly engageable with a female threaded portion at the end (the box end) of another section of pipe.
The ends of the pipe, including the threads, are subject to damage when not in actual use, such as from contact with other objects, or from being dropped, during transportation and storage. Such damage may render the pipe faulty or unusable, resulting in delay, hardship and increased expense. Devices known as "thread protectors" are commonly used to protect the ends of the pipe, particularly the pipe threads thereon, from such damage. A "pin end" thread protector is connected to and protects the pin end of the pipe and a "box end" thread protector is connected to and protects the box end of the pipe. The thread protectors are designed to prevent damage to the respective pipe ends when the pipe impacts other objects, the ground or otherwise is subjected to external impact. Example prior art thread protectors are disclosed in U.S. Pat. Nos. 4,957,141; 5,195,562; and 5,244,015, all to Dreyfuss et al., and 4,809,752 to Strodter, all of which are hereby incorporated herein by reference in their entireties.
An industry standard for thread protectors for premium pipe is the "Shell.RTM." test. A specification for the Shell test entitled "Shell Oil Specification for Thread Protectors March 1988" is attached hereto and hereby incorporated herein by reference in its entirety. The Shell test is also described in Technical Paper ADC/SPE 17209 entitled "Performance Evaluation of Commercially Available Thread Protectors," authored by E.J.C. Spruijt and also hereby incorporated herein by reference in its entirety (the first two pages of the Paper are attached hereto). The Shell test subjects the thread protector and pipe to an impact energy to determine if the thread protector being tested can protect the pipe ends from damage. One type of Shell test simulates installing the thread protector on the pipe, raising the pipe off the ground, and then dropping the pipe axially to evaluate the effectiveness of the thread protector by determining whether the end of the steel pipe was damaged. The Shell test requires that the thread protector prevent the pipe ends from damage during different tests at varying temperatures. Since the pipe is used in various environments and thus exposed to a wide range of temperatures, the test is performed at varying temperatures, such as 150.degree. F., 70.degree. F. or ambient, and -50.degree. F., to insure that the thread protector will protect the pipe when exposed to heat or cold over time. For testing pipes having nominal outer diameters of between 4 inches and 8 3/4 inches, for example, the thread protector and pipe may be subjected to 1200 ft/lbs of energy at temperatures of 150.degree. F. and again at 70.degree. F. (ambient). A third test subjects the thread protector and pipe to 600 ft/lbs of energy at a temperature of -50.degree. F. For example, a section of pipe having a nominal outer diameter of between about 4.0 inches and about 8 3/4 inches with a weight of 430.4 lbs is dropped 33.6 inches transmitting 1205 ft/lb of impact energy onto the thread protector and pipe end. To determine the protective capacity of the protector, the pipe is inspected for damage. Damage may include dents, damaged threads, out-of-roundness, or other damage affecting the use of the pipe in the field. Although it is preferred that the thread protector not be damaged, damage to the thread protector is not a criteria in the Shell test. The Shell test for larger diameter pipe requires a larger impact, such as 1500 ft/lbs at 150.degree. F. and 70.degree. F. or ambient, and 800 ft/lbs at -50.degree. F.
The thread protector must prevent substantial impact energy from reaching the pipe end to adequately protect the pipe from the impact energy. Prior art thread protectors have been designed as strong as possible to withstand the anticipated impact energy. Thus, prior art thread protectors are large, sturdy and rigid members which will prevent damage to the pipe and to the thread protector itself.
To provide this strength and rigidity, many prior art thread protectors are constructed of a composite of steel and plastic. One of the most commercial thread protectors is manufactured by Drilltec Patents and Teclmologies Company, Inc. and is known as Drilltec's ESPS.TM. protector. This protector includes an outer steel sleeve crimped over an inner plastic member. The steel sleeve has the effect of providing stiffness and rigidity to the protector, enabling it to withstand impact energy. The Drilltec protector is disclosed in U.S. Pat. Nos. 4,957,141; 5,195,562; and 5,244,015. Other prior art thread protectors, such as Drilltec's STP.TM., Drilltec's SSP.TM. and Molding Specialties, Inc.'s Magnum model thread protectors are constructed of plastic and often include additives such as fibers or particles of another material, but without a steel sleeve. FIGS. 1A and 1B illustrate a pin end thread protector and a box end thread protector, respectively, similar to that manufactured by Molding Specialties, Inc. for a pipe having a nominal outer diameter of 7 inches.
The prior art thread protectors are believed to have various disadvantages. Because these protectors are large and heavy, they require a substantial quantity of material, typically both steel and plastic, for their construction. The more material that is required to produce the protector, the greater the manufacturing cost. Prior art protectors are thus expensive. Further, the larger, bulkier and heavier the protector, the more difficult and time consuming the handling of the protectors and the greater the need for special handling equipment, particularly for large diameter pipe thread protectors.
Additionally, various prior art thread protectors constructed without a steel sleeve are believed to warp and become out-of-round or deformed, thus making it difficult or impossible for them to be installed onto the pipe end, thereby decreasing their usefulness. Further, typical prior art thread protectors constructed primarily of plastic are believed to be generally ineffective at withstanding significant impact energy. In particular, typical prior art thread protectors constructed of all plastic material, or plastic containing particles of other material, are believed to generally not pass the Shell test without being beefed up in size so as to use a substantial amount of material, thus substantially raising the cost of manufacturing the protector.
Thus, there remains a need for a thread protector capable of protecting pipe ends that requires less material and is thus more cost effective to manufacture (material and labor) than prior art thread protectors. Preferably, the thread protector does not include a steel sleeve and may be made of a material lighter than steel. Ideally, the thread protector could be designed to plastically deform under impact so that the impact energy is transformed into internal friction and thermal energy; the thread protector thus using up or substantially reducing the transmitted energy and preventing the energy from reaching or damaging the threads of the attached pipe. Especially well received would be a thread protector that is made substantially of plastic and that passes the Shell test. Further, the thread protector is preferably reduced in size and material than many prior art thread protectors, thereby reducing shipping and handling requirements.
The present invention overcomes one or more of these deficiencies in the prior art.